Muscle engagement for intense, short-duration effort relies initially on the phosphocreatine system.

“Muscle. Muscle is going to engage and generate energy first by using this phosphocreatine system. High bouts of effort, really intense effort, short-lived, seconds to minutes, but probably more like seconds, it's going to be this phosphocreatine, literally a fuel source in the muscle that you're going to burn just like you would logs on a fire.”